Conventional heating or cooling systems require energy from limited resources, e.g., electricity and natural gas, which have become increasingly more expensive and are at times subject to shortages. Much attention has been given to sources of energy that exist as natural phenomena. Such energy includes geothermal energy, solar energy, tidal energy, and wind-generated energy. While all of these energy sources have advantages and disadvantages, geothermal energy, i.e., energy derived from the Earth or ground, has been considered by many as the most reliable, readily available, and most easily tapped of the natural phenomena.
Ground water-based geothermal systems have been used with heat pumps or air handling units to satisfy building HVAC (heating, ventilation, and air-conditioning) loads. These systems are favored because geothermal systems are environmentally friendly and have low greenhouse emissions.
The use of vertical water wells as a thermal source/sink for efficient ground source heat pump (GSHP) operation has been in substantive practice since the 1980s. The most often specified system today is a closed loop system that employs polypipe grouted into the wellbore. These grouted loop (GL) systems operate with a secondary heat transfer fluid between the well bore and the heat pump (HP) heat exchanger. While GL systems offer relatively low maintenance over the lifetime of the installation, the high initial cost of the well field is a handicap to universal acceptance.
Standing column well (SCW) systems, on the other hand, operate as traditional water wells. Each well requires its own pump, which at some point will require replacement. SCW can operate in an open loop or closed loop mode. Traditionally, an open loop system requires a minimum of two SCW, one that supplies water to a building and the other that receives or accepts the return water, a so-called “pump & dump” operation. SCW can also be configured in a closed loop, i.e. returning water originally supplied from the well back to the same well. The benefit of the latter system is that it maximizes heat transfer to the well bore rock, provided that the entire length of the well is used in the heat exchange, a mechanism described in U.S. Pat. No. 5,183,100, incorporated herein. Because of this improved heat transfer, SCW systems require typically half the number of wells drilled as closed loop systems. This translates into significant initial savings to the owner.
In reviewing prior SCW system installations, Applicant has realized the presence of an opportunity to make improvements in the well field components, the installation and the operation of the system, which can be expected to further reduce the installed cost of the system, while moving toward standardization and a set of best practices. The subject of the present application is especially relevant to large installations that provide the best opportunity to demonstrate significant cost advantages. The present application focuses on the well field design, operation, components and installation practices to affect an optimal, low cost solution, insuring equal return water distribution to the active wells, and creating standardization and a set of best practices.